Conjugated diene rubbers (for example, styrene-butadiene copolymers) obtained by emulsion polymerization methods are known as rubbers for automotive tire applications. A variety of conjugated diene rubbers that can realize an excellent fuel efficiency performance have been introduced in recent years amid the expectations for improved automotive fuel efficiencies.
As an example, a conjugated diolefin (co)polymer rubber with the following characteristics (1) to (3) has been proposed: (1) it is a (co)polymer rubber of a conjugated diolefin or a conjugated diolefin and an aromatic vinyl compound; (2) it has a primary amino group and an alkoxysilyl group bonded in the (co)polymer chain; and (3) an at least difunctional monomer is copolymerized in the (co)polymer chain, and/or, at least a portion of the (co)polymer chain is coupled with an at least difunctional coupling agent (see Patent Reference 1).
In another example, a modified diene polymer rubber is proposed that is obtained by a step 1 of obtaining an active polymer having an alkali metal terminal by polymerizing a conjugated diene monomer or a conjugated diene monomer and an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal catalyst, and a step 2 of obtaining a modified polymer rubber by reacting the active polymer with a compound that has a specific formula (see Patent Reference 2).
A method has also been proposed for producing a modified polymer that has an increased interaction with silica and carbon black and that can provide improved failure characteristics and wear resistance and an improved low heat build-up performance. This method proceeds through a primary modification reaction, in which a hydrocarbyloxysilane compound is reacted with the active site of a polymer that has an organometal active site in the molecule, and through a subsequent secondary modification reaction, in which a hydrocarbyloxysilane compound is reacted via a condensation reaction between hydrocarbyloxysilyl groups (see Patent Reference 3).